The role of adrenergic receptors in cardiovascular changes associated with exercise in salmon

1. 1. Intravenous injections of epinephrine produced an increase in dorsal aortic blood pressure and heart rate. Low dose levels of epinephrine caused a reflex slowing of the heart, a response abolished by atropine injections into the pericardial cavity. 2. 2. Phenoxybenzamine injections blocked the pressor response to epinephrine. Changes in blood pressure during activity and excitement also disappear after α-adrenergic receptor blockage with phenoxybenzamine. 3. 3. It is concluded that there are α-adrenergic receptors in blood vessels in the gills and in the general body circulation. Epinephrine probably causes a vasodilation in the gills and a vasoconstriction of blood vessels peripherally in the systemic circulation. 4. 4. Blood pressure changes occuring during swimming can be explained by the interaction of epinephrine with α-adrenergic receptors. 5. 5. Dichloroisoproterenal or propranolol, when injected intravenously in fish, had little effect on the response of the heart to epinephrine, but caused a marked fall in dorsal aortic blood pressure and heart rate.